This invention relates to data backup and data recovery for a computer system.
In order to reduce the risk of losing data stored in a storage system due to a disaster or a failure, a method of creating and storing a copy of the data stored in the storage system is known. As techniques of creating a copy, there are a backup and restore technique and a remote copy technique, both using a journal.
For example, the following technique is known as the backup and restore technique using a journal. In other words, a storage system maintains a journal of a plurality of journal entries and at least one snapshot of one or more data volume. By assigning a unique sequence number to each of the journal and the snapshot in the order of occurrence, it becomes easy to find out a journal to be applied to the snapshot. In this manner, an overflow condition causing the exhaustion of a journal space is detected to recover the journal space, as described in JP 2005-18738 A.
The following technique is known as the remote copy technique using a journal. In other words, at least two secondary storage systems are connected to a primary storage system connected to an upstream device. The secondary storage systems read out journals of data update from the primary storage system at their own timings so as to save the read journals in predetermined logical volumes. Then, the secondary storage systems create copies of the data in the primary storage system based on the journals stored in the virtual volumes at their own timings so as to store the copies in secondary virtual volumes. The primary storage system retains the journals until both the secondary storage systems read and restore the journals. The timing of journal read is controlled according to the quantity of journals, a processing load and the like, as described in JP 2005-174196 A.